Fail gracefully when Metal encounters a geometry shader.

Change-Id: I452e52a87d89cefb5c21a0d9d57e9771f3038d73
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/319783
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
6 files changed